sun damage

Damage that occurs to a hide or skin when it
becomes heated above a certain critical
temperature while it is still moist and is laid
out in the sun to dry (cure). A completely dry
skin can become very hot and still not be affected
under normal conditions of cure, but prior to this
a skin is very susceptible to damage. Also, the
drying of a salted skin proceeds so uniformly
throughout its entire thickness that the cooling
effect produced by evaporation off its surfaces
maintains the temperature of the entire skin below
the danger point until it is uniformly dry.
Without salt, however, a skin tends to dry
unevenly when laid out in the usual manner, which
is flesh side up. This can happen because the
flesh side can dry out completely and begin
generating heat, while the underside remains
moist, and, being shielded from evaporation, also
begins to generate heat. This is especially the
case when pieces of flesh, generally of a fatty
nature, are present on the flesh side, and further
retard the drying of areas beneath them. The
result of overheating moist skins is to "cook,"
and therefore gelatinize, the skin fibers, so that
they are no longer leather-forming collagen. The
damage, however, is not visible in the dried skin,
nor can it be detected even after the skin is
soaked to return it to the pre-cured condition. It
is only after liming that the damaged areas tend
to disintegrate, leaving holes in the skin, that
the damage becomes apparent. In many cases the
damage is largely limited to the grain surface,
which becomes deeply corroded, giving rise to the
trade term "blister" for this particular type of
damage. See also: PUTREFACTIVE DAMAGE .